Streams and lakes are losing water when their surface is higher than the regional water table. The seepage flux depends on the surface water level, the geometry and hydraulic properties of the streambed and the underlying aquifer, as well as on the position of the regional water table. In particular, when naturally or artificially lowering the latter, surface water eventually disconnects from groundwater, resulting in an unsaturated zone in-between both saturated components.

Here we first study the one-dimensional configuration, for which disconnection requires the presence of a clogging layer, i.e., a layer having a lower permeability than the underlying sediments. We provide asymptotic solutions to the steady-state Richards equation for generic unsaturated hydraulic conductivity functions. The solutions are readily applicable to common parametrizations, such as van Genuchten or Brooks and Corey. The identification of three regimes, one dominated by the clogging layer, one by the underlying sediments and one balanced by both layers, motivates a refined classification of clogging. We also argue that infiltration rate roughly grows linearly with ponding depth. Some applications based on these findings are proposed, such as novel formulas for seepage modeling, a method to identify disconnection and a capillary zone height estimation formula. For multidimensional seepage, disconnection is also possible without clogging layer, but this eventuality is often discarded. Considering a generic seepage problem, we introduce a framework based on constitutive relations to qualitatively define all possible seepage states. Recognizing the need to quantify these relations to improve our ability to identify seepage states, we advocate for simple models to compute them.

Despite their proximity with glaciers, terraces of glacial forefield are often water scarce due to high sediment permeability and groundwater disconnection. Microbial mats are thought to contribute to primary succession in these nascent ecosystems, notably by impermeabilizing tributary streams and, thus, increasing water retention. Here, this biogeomorphic potential is explored in two steps. First, observations of very similar microbial mat thickness and permeability dynamics from a series of outdoor flume experiments mimicking tributary conditions, suggest relative clogging homogeneity within the considered streams. These experiments also highlight daily cycles of permeability caused by photosynthetic activity. Furthermore, we show that the permeability is not strongly affected by desiccation and identify a potential evaporative pumping mechanism driven by microbial mats. Second, an idealized terrace model, based on one-dimensional seepage solutions, is introduced to assess under what conditions surface water extent is expected to be significantly affected by clogging. The ratio between flooded distances within clogged and unclogged channels is shown to be almost independent on the inflow for sufficiently shallow streams, to scale sublinearly with the clogging resistance for intermediate clogging and to converge to a maximum value for larger clogging. The overall effect of microbial clogging on water retention on glacial forefield terraces remains poorly constrained, because strongly sensitive to the permeability of the underlying sediments. Field and experimental measurements are suggested to fill this gap.